טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMikhaylov Natalia
SubjectAntimicrobial Magnesium Coatings on Stainless Steel
Implants
DepartmentDepartment of Materials Science and Engineering
Supervisor Research Professor E Dan Shechtman
Full Thesis textFull thesis text - English Version


Abstract

The development of microbial colonies on the surface of medical implants is a serious problem. Microbes, find their way into the host during the operation, and may irreversibly adhere to the surface of the implant. Once the bacteria adhere, they can multiply, form complex multilayered colonies, and produce a slimy matrix material that encases the bacterial cells. Called a biofilm, this structure is difficult and often impossible to eradicate in the body with antibiotics, because the slime matrix acts as a physical and chemical barrier to protect the bacteria. The best timing for dealing with medical implant induced infections is during the several hours that follow the operation. The methods used today to prevent biofilm formation are antibiotics or silver ions releasing coatings. However these coatings may present a problem due to toxicity. Moreover, many antibiotics operate specifically and show limited efficacy against certain bacterial strains. Magnesium metal present in a vicinity of the implant may solve the problem, since it has been shown to possess antibacterial properties due to formation of magnesium hydroxide during the corrosion process. The main objective of this research was to develop a process for coating 316LVM stainless steel implants with thick magnesium film, for the protection of implant’s surface from infection thanks to gradual dissolution of the coating during the critical post-operative hours. We have sputtered and thermally evaporated pure magnesium coatings on 316L stainless steel Kirschner wires. The thermal evaporation process was carried out in a system built for this purpose at various substrate temperatures. The films’ morphology was studied using SEM and corrosion tests were performed in stimulated body fluids and in phosphate buffered saline. The evaporated films’ density and corrosion performance depends on the substrate temperature during evaporation. Adatom diffusion rate rises with rising substrate temperature, and high diffusion rate causes grain growth and coating densification. Additionally, a protective oxide film is formed at higher substrate temperatures. Coating densification and the presence of a protective film are the reasons for improved corrosion performance. Coatings evaporated at substrate temperatures above 300°C may be suitable for reducing infection during the critical short term post-implantation period.